There is a substantial need for non-pressure pipe useful for the transport of rainwater and sewage away from residential and commercial properties. Typically, pipes of this nature are buried underground and are made of clay or metal. Each of these materials, though, is susceptible to the environment in which it resides. Clay pipes, for example, often contain junctions that allow the infiltration of roots or other materials that may clog the pipe or otherwise damage the piping system over time. Similarly, metal pipes are susceptible to corrosion.
In recent years, these issues have been addressed to some extent via the adoption of pipes made of materials such as polyvinyl chloride and polyethylene (HDPE). Even more recently, non-pressure pipe manufacturers have been employing polypropylene as a substitute material. See, e.g., U.S. Pat. No. 6,933,347 which discloses a polypropylene pipe comprising an impact copolymer; U.S. Pat. No. 6,433,087 which also discloses a pipe comprising an impact copolymer, and United States Patent Publication 2007/0117932 which teaches a heterophasic polyolefin composition comprising an elastomeric polymer in combination with a crystalline polymer having a broad molecular weight distribution.
The widespread adoption of polypropylene non-pressure pipes in the United States has, however, been slow. Specifically, although polypropylene provides an affordable alternative to polyethylene, and is easily fused to provide essentially seamless pipes of variable length, the performance characteristics of the pipes produced from presently available resins have not been ideal. Moreover, presently available polypropylene resins suitable for manufacturing pipe are difficult to process.
For example, polypropylene pipes made from resins that are currently available may deform if buried too deeply, impeding the flow of the rain water or sewage being transported. These failures are believed to be due, in part, to an industry wide focus on developing resins having specific flexural moduli and notch impact strengths. These properties, though, do not accurately predict long term performance of buried polypropylene structures as both flexural moduli and notch impact strength relate only to short term performance.
Thus, what is needed is a resin exhibiting good long term performance for use in buried structures, particularly corrugated non-pressure pipe. In particular, it has been found that what is needed is a resin exhibiting good long term creep performance, good creep rupture strength, and a good balance of stiffness and impact resistance. The present disclosure provides such a resin.